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2. Heat is the thermal energy transferred from one object to another due to differences in temperature. Heat energy is measured in joules (J). There is no direct method used to measure heat so indirect methods must be used.

Internal or Thermal Energy is symbol by U and has the SI unit of the Joule (J).
It is the sum of all the energy (Kinetic and Potential energies) an object possesses. Kinetic energy refers to the movement of the particles in a body. Potential energy refers to the gravitational and electrostatic forces that exist between particles. It is not possible to measured the internal energy of a body but only changes in internal energy.

Temperature is a measure of the average kinetic energy of the molecules of a substance. Temperature measures how hot or cold an object is with respect to a standard. Temperature can be measured with a thermometer.

The kinetic theory can be used to clearly distinguish between temperature and thermal energy. Temperature is a measure of the average kinetic energy of individual molecules. Thermal energy refers to the total energy of all the molecules in an object.

3. The concept that matter is made up of atoms in continual random motion is called the kinetic theory. We assume that we are dealing with an ideal gas. In an ideal gas, there are a large number of molecules moving in random directions at different speeds, the gas molecules are far apart, the molecules interact with one another only when they collide, and collisions between gas molecules and the wall of the container are assumed to be perfectly elastic.

Temperature is a measure of the average kinetic energy of the molecules of a substance.
Particles in a hot body have more kinetic energy than those in a cold body so it can be said that as temperature increases, kinetic energy increases. If the kinetic energy rises, the molecules move at greater speeds. If the volume remains the same, the hotter molecules would be expected to hit the walls of the container more frequently than the cooler ones, resulting in a rise in pressure

4. One way a thermometer can be calibrated is by the amount of thermal expansion and contraction
that occurs within a given type of substance.
The conventional liquid-in-glass thermometer was invented in the seventeenth century. This bulb-and-tube device is still in use; it is shown in the Figure below.

In these thermometers the diameter of the bulb is much greater than the diameter of the tube so that a small change in the volume of liquid in the bulb will produce a large change in the height of the liquid in the tube.

Thermometers are limited by the physical properties of the substance from which they are made.
(i.e., An alcohol thermometer is of little use above the boiling point of alcohol, and a mercury
thermometer will not be of any use below the freezing point of mercury.)

Temperature Scales The most common scale is the Celsius (or Centigrade, though in the United States the Fahrenheit scale is common.) Both of these scales use the freezing point and boiling point of water at atmospheric pressure as fixed points. On the Celcius scale, the freezing point of water corresponds to 0°C and the boiling point of water corresponds to 100°C. On the Farenheit scale, the freezing point of water is defined to be 3°F and the boiling point 212°F. It is easy to convert between these two scales by remembering that 0°C = 32°F and that 5°C = 9°F. The Kelvin scale is based upon absolute zero (-273.15 °C), or 0 K.

Triple Point: The triple point of water serves as a point of reference. It is only at this point (273.16 °K) that the three phases of water (gas, liquid, and solid) exist together at a unique value of temperature and pressure.

Temperature is a property of a system that determines whether the system will be in thermal equilibrium with other systems.

5. The Celsius scale is commonly used to measure temperature. Its scale has been calibrated to the
physical properties of pure water. The normal freezing point of water was arbitrarily set as 0 °C and
the normal boiling point of water was arbitrarily set at 100 °C. Arithmetic gradations represent
uniform temperature changes on the scale. Note that Celsius is captalized since this was the name of a person (Anders Celsius).

There is another temperature scale which is very important in gas behavior. It is called the Kelvin
scale (symbol = K). Note that K does not have a degree sign and Kelvin is captalized because this
was a person's title (Lord Kelvin, his given name was William Thomson). The Kelvin scale, also called the Absolute scale, sets 0 K as absolute zero (-273.15 °C). Temperature increases on the scale are the same as on the Celsius scale (1 K = 1 C°).

Conduction is the transfer of heat by the passing of internal energy from one particle to another as adjacent particles collide. Heat is transferred by these collisions. Conduction only occurs in solids. Good conductors of heat are those whose particles are close together, hence more likely to collide, eg metals. Poor conductors of heat are usually insulators as they are usually less dence an the particles are often unable to move, eg plastics. The best example of this phenomena would be to take a metal bar and heat one end of it. The other end will get warm and then hot through conduction. When you put a metal pan on the stove, the inside of the pan gets hot through conduction of the heat through the metal in the bottom of the pan. It is impossible for heat to travel by conduction in a vacuum. For this reason a vacuum can be used to stop heat flow by conduction in a thermos flask.

Convection is the transfer of heat through a fluid by the actual flow of the heated fluid. The flow is caused by different densities at different temperatures. Hot fluids and gases generally rise.

Radiation consists of electromagnetic waves which act as a medium to transfer energy from one source to another. When absorbed, most radiation becomes internal energy. A surface that is dark and rough will absorb most of the radiation. A surface that is light and shiny will reflect most of the radiation. A good absorber of radiation is also a good emitter of radiation. When infrared is absorbed it results in atomic motion, and therefore in a rise in temperature. Some common examples of infrared: heat you feel radiating from an electric heater or a red-hot piece of metal, heat you feel radiating from the bricks in a fireplace even if the fire has gone out, heat you feel radiating from a concrete wall after the sun has gone down.

Conduction and convection require the prescence of matter. Radiation consists of electromagentic waves hense is able to transfer energy through a vacuum.

When different parts of an isolated system are at different temperatures, heat will flow from the part at a higher temperature to that at the lower temperature until they are at thermal equilibrium

(Top) heat flows from the hot end to the cool end of the rod. As the distance from the burner flame increases, the temperature of the rod falls by a proportional amount. In a tea kettle (bottom left), hot water rises and cold water descends until all the water is at the same temperature. A home heating lamp (bottom right) produces its heating effect by direct transfer of radiant energy.

7. Some theories are based on supporting postulates. A postulate is a statement which is agreed on by consensus among scientists.
The following are important postulates of the kinetic molecular theory:
1. All matter consists of atoms.
2. Atoms may join together to form molecules.
3. Solids usually maintain both their shape and their volume.
4. Liquids maintain their shape, but not their volume.
5. Gases do not maintain shape or volume. They will expand to fill a container of any size.
6. Molecular motion is random.
7. Molecular motion is greatest in gases, less in liquids, and least in solids.
8. Collisions between atoms and molecules transfers energy between them.
9. Molecules in motion possess kinetic energy.
10. Molecules in gases do not exert large forces on one another, unless they are colliding.

As information is acquired in science, new theories can develop, or existing theories can be further
supported, modified, or rejected. Many observable phenomena give support to the kinetic molecular theory. A theory is a system of ideas or a sphere of abstract knowledge which attempts to explain why certain phenomena occur, whereas a law is a statement of specific conditions or relationships that exist in nature. Models are useful in science to illustrate abstract or complicated concepts.

Although heat at first appears to have nothing to do with motion, it is now understood that heat is the motion of molecules. The connection between heat and motion was provided by Benjamin
Thompson (1753-1814), an American who sympathized with the British during the Revolutionary War and eventually settled in Bavaria and became Count Rumford. While watching the boring of artillery cannons in Munich in 1798, he concluded that motion could be transformed into heat and estimated the mechanical equivalent of heat. Half a century later the experiment was refined and repeated by James Prescott Joule (1818-1889), the son of an English brewer. Joule's careful quantitative measurements became a model for modern science. The calorie is defined as the amount of energy needed to raise the temperature of one gram of water at 14.5° one degree Celcius.

8. If volume is kept constant, the pressure of a unit mass of gas is proportional to temperature. If temperature increases so will pressure, assuming no change in the volume of the gas.
Holding pressure constant, causes the volume of a gas to be proportional to temperature. Thus, increasing temperature of a unit mass of gas causes its volume to expand along as there is no change in pressure. The Kelvin temperature of a gas is directly proportional to its kinetic energy. Double the Kelvin temperature, you double the kinetic energy.

In the kinetic-molecular theory of gases, pressure is the force exerted against the wall of a container
by the continual collision of molecules against it. It is assumed that the molecule rebounds elastically and no kinetic energy is lost in a perpendicular collision

All gas law problems need to be done with Kelvin temperatures. You can convert between Celsius and Kelvin like this: Kelvin = Celsius + 273.15. Often, the value of 273 is used instead of 273.15. For example, 25 °C = 298 K, because 25 + 273 = 298.

9. When you squeeze on a balloon to increase the pressure, the volume of the balloon goes down.
When you heat a balloon the volume of the balloon goes up

10. Boyle's Law
Robert Boyle worked with the pressure of gas. Boyle's Law is used when the pressure of a gas changes. Simply stated, Boyle's Law indicates that for a fixed amount of gas (fixed number of moles) at a fixed temperature, the pressure exerted by a gas varies inversely with its volume.
If the volume of a container decreases, pressure of the gas increases.
If the volume of a container increases, pressure of the gas decreases.
(When you squeeze on a balloon to increase the pressure, the volume of the balloon goes down.)

For a particular sample of any gas, Boyle's law can be shown graphically as is done in the diagram above. It is more common to express it mathematically as P1V1 = P2V2 or as PV = k, where k is a constant which depends upon the particular sample.

Charles' Law
French chemist Jacques Charles studied the relationship of temperature and volume of gases. Charles' Law is used when the temperature of a gas changes. Simply stated, Charles' Law indicates that for a fixed amount of gas (fixed number of moles) at a fixed pressure, the volume of a gas varies directly with the Kelvin temperature.
As the temperature of a gas increases, the volume of the gas increases.
As the temperature of a gas decreases, the volume of the gas decreases.
In other words, as the temperature increases, the volume increases. (When you heat a balloon the
volume of the balloon goes up.)

It is more common to express it mathematically as V₁/T₁ = V₂/T₂ or as V/T = k, where k is a constant which depends upon the particular sample.

The Combined Gas Law:
The Combined Gas Law is used when both pressure and temperature change. It is a combination of Boyle's Law and Charles' Law. The Combined Gas Law is expressed by the equation:
P₁V₁/T₁ = P₂V₂/T₂

Stawa Set 14

Physics Study Guide 46

11. Example Problems using Boyles Law:
Question: Consider a balloon with a volume of 22.4 L at 273 K and 1.00atm. What will be the new volume if the pressure is doubled to 2.00 atm?
Solution: Using Boyles Law and solving for V2 we get:
                     P₁V₁                  (1.00 atm)(22.4 L)
              V₂ = ----             V₂ = -------------------
                       p2                      (2.00 atm)
          Or, V₂ = 11.2 L

An Example Problem using Charles' Law
Question: Consider a balloon with a volume of 22.4 L at 273 K. What will be the new volume if the temperature increases to 298 K?
Solution: Using Charles' Law and solving for V2 we get:
                  V₁T₂                (22.4 L)(298 K)
         V₂ = -----          V₂ = ---------------
                    T₁                     (273 K)
           Or, V₂ = 24.5 L

12. Notice how heat transfers easily through the metal pan to warm the food however the insulated handle however remains cool.

Gases are poor conductors of heat. They are in fact excellent insulators and are often used to prevent or reduce the movement of heat by conduction. Such examples of its insulating ability can be shown by:
- Clothing such as woolen pull-overs and vests: It is the air within the clothing which reduces the heat loss from your body hence keeping you warm.
- Double Glazing: Glass is a poor conductor of heat but it is thin layer of air trapped between the two sheets which makes double glazing a very effecient means of reducing heat loss through windows.
- It is impossible for heat to travel by conduction in a vacuum. For this reason a vacuum can be used to stop heat flow by conduction in a thermos flask.

Sea Breezes: Sea Breezes along the coast are convection currents set up by the heat from the sun. During the day time, the land becomes warmer then the sea. The air immediately above it becomes warm and becomes less dense. Cooler more dense air from over the sea moves in forceing the warm less dense air to rise.

A thermos flask is a double-walled bottle with silvering on the inner side of each wall with vacuum in between. Any substance, hot or cold, put inside the flask remains so for a considerable period as there is a no exchange of heat due to radiation because of the silvering nor due to conduction or convection. Vacuum is a non-conductor and non-medium. Thermos flask is generally used for preserving hot tea, coffee or ice, cold Drinks, etc.

You can see in the diagram two paths for heat transfer. The cap and the walls. Cork or plastic stopper is used to prevent further loss of heat.

A vacuum in the space between the inner and outer bottles prevents heat from passing through the bottle. The vacuum between the bottles slows down the transfer of heat by convection. In order to reduce the transfer of heat by radiation, the facing surfaces of the glass bottles are coated with a silvery solution of aluminium which reflects heat.

Water exhibits anomalous behaviour. From 0 °C to 4 °C it contracts as heated. It also expands
when it freezes. The expansion results in a decrease in density, allowing ice to float on water. Also,
water has a high specific heat capacity compared to other liquids.

Physics Text book pg 104

The unique physical characteristics of water lead to many interesting and important applications.
(Several should be discussed. Wherever possible, suggest some of the environmental implications of
these characteristics of water.)

Stawa Set 10 + 12

Physics Text book pg 119-120, 129, 137-139

Physics Study Guide 54-60

13. The Specific heat capacity is a characteristic of the material. It is the quantity of heat (measured in Joules) required to raise the temperature of one kilogram of the material by one degree Celcius or one Kelvin

or, Q = mcDT
where Q is the change in heat content in Joules,
m is the mass in kg,
c is the specific heat capacity in J/(kg°C),
DT is the change in temperature in °C or K.
The derived unit for c, the specific heat capacity, is J/(kg°C)
The units J/kg K are the same as J/kg°C

The specific heat capacity of a substance depends on its molecular structure and on its phase.

The specific heat capacity of a specific substance

Ice : 2060 J/kg K	Water : 4180 J/kg K	Steam : 2020 J/kg K
Copper : 390 J/kg K	Silver : 230 J/kg K	Aluminum : 900 J/kg K
Iron : 450 J/kg K

Notice that the specific heat of water is very high - higher than ice and steam. Water has a very high specific heat, meaning that it heats slowly and cools slowly.

The specific heat of a material yields information about how the material heats and cools. If you add ten joules of heat to two materials, the one with the lowest specific heat will show the greatest temperature change. If you cool two materials ten degrees, the material with the greatest specific heat loses the most energy.

The specific latent heat of a substance is the quantity of heat energy required to change the state of
a unit mass of a substance. The SI unit for specific latent heat is J/kg.

At a phase change, the amount of heat given off or absorbed is found using:
Q = mL where
Q is the heat transfered in joules.
L is the latent heat in in joules per kilogram.
m is the mass, in kilograms

14. At a phase change, the amount of heat given off or absorbed is found using:
Q = mL where
Q is the heat transfered in joules.
L is the latent heat in in joules per kilogram.
m is the mass, in kilograms

Q = mcDT
where Q is the change in heat content in Joules,
m is the mass in kg,
c is the specific heat capacity in J/(kg°C),
DT is the change in temperature in °C or K.

15. The three most common states of matter are solid, liquid, and gas. When heat is added to a substance, one of two things can occur. The temperature can increase or the material can change to a different state.

A phase change is a change from one state of matter (solid, liquid or gas) to another. For pure substances the temperature remains constant as phase change occurs. The temperature will change while a substance is in a particular phase. For a phase change to occur or for a substance in a particular phase to change to have a change of temperature energy must be added or taken away.

This can be observed in the above graph showing the phase changes of pure water at one atm of pressure.

During melting and freezing the temperature is constant at 0 ºC (at 100 ºC for vaporization and condensation) but energy is being added or taken away. During the liquid phase both temperature and energy change from point to point along the line.

Solid	Solid/Liquid	Liquid	Liquid/Gas	Gas
Increase in KE	Increase in Phase	Increase in KE	Increase in Phase	Increase in KE
D Temperature	D Phase	D Temperature	D Phase	D Temperature
Q= MCDT	Q=ML_F	Q= M₂CDT	Q=ML_V	Q= M₃CDT
Melting Point -->	<--Freezing Point	Boiling Point -->	<-- Condensation Point

When a material changes phases from solid to liquid or from liquid to gas, a certain amount of energy is absorbed (in the reverse process, the heat is given off). Let's look at ice (a solid) at a temperature of -5°. When heat is added to ice, its temperature increases until it reaches 0°. At this point, ice begins to melt--it changes its state from a solid to a liquid. The temperature remains constant at 0° until all the ice has melted. Now we have water at 0°. As heat is added to the water, its temperature increases until it reaches 100°. At this point, the water begins to boil, changing its state from liquid to gas. The temperature remains constant at 100° until all the water boils, turning into steam. Now we have steam at 100°. If you continue to add heat, the temperature of the steam begins to increase.

The specific latent heat of a substance is the quantity of heat energy required to change the state of
a unit mass of a substance. The SI unit for specific latent heat is J/kg.

Heat of fusion (Hf) : The specific latent heat of fusion is the quantity of heat energy released when 1 kg of a substance solidifies (i.e. fuses) without changing its temperature. It is also said to be the amount of energy needed to change 1 kg of a substance from a solid to a liquid. For water, Hf=333,000 J/kg (333 x 103 J/kg) or 3.33 x 105 J/kg. Water has one of the largest specific latent heats of fusion of all substances.

Heat of vaporization (Hv): The specific latent heat of vaporization is the quantity of heat energy needed to vaporize (change from a liquid to a gas) 1 kg of a substance without changing its temperature. For water, Hv = 2,260,000 J/kg K (or 2.26 x 106 J/kg) or 22.6 x 105 J/kg

If energy is added to a system heating it and causing an increase in temperature, energy is positive; if energy is removed from a system cooling it and causing a decrease in temperature, energy is negative. If energy is added to a system causing a change in the state of matter from a solid to a liquid or from a liquid to a solid, that energy is positive. If energy is removed from a system causing a change in the state of matter from a gas to a liquid or from a liquid to a solid, that energy is negative.

Sublimation is the process whereby a solid changes directly to a gas without passing through the liquid phase.

Evaporation can be explained in terms of the kinetic theory. The fastest moving molecules in a liquid escape from the surface, decreasing the average speed of those remaining. When the average speed is less, the absolute temperature is less. Thus evaporation, the escaping of the fastest moving molecules from the surface of a liquid, is a cooling process.

Boiling: When the temperature of a liquid equals the point where the saturated vapor pressure equals the external pressure, boiling occurs.

16. When substances that have varying temperatures are put together, there will be an exchange of heat. Due to the law of conservation of energy (In any transformation of energy, the total amount of energy remains constant) we can say Heat gain = Heat Lost. It is possible that more than one substance gains heat, hense all possibilities must be considered. Therefore using the formulas for specific heat and latent heat we can determine the level of heat exchange. ie Q=MCDT and Q=ML

Whenever two substances at different temperatures are allowed to mix, heat travels from the hotter
substance to the colder one. The quantity of heat given off by the hotter substance is equal to the
quantity of heat energy gained by the cooler object, provided that heat energy does not escape to
the surroundings. The transfer of energy will continue in this way until both substances reach the
same temperature. The is called the Principle of Heat Exchange.
Heat_Lost = Heat_Gained

A Calorimeter is a device used to measure changes in thermal energy. A calorimeter is an insulated container used to make a precise measurement of heat exchange.

When energy is converted from one form to another the ability to do work can only be lost, and
never gained. That is, no device transfers its heat energy completely into work. For that reason, it is
impossible to build a perfect heat engine. (A heat pump requires an application of work to transfer
heat energy from a low temperature to a higher temperature. Thus, the Second Law of Thermodynamics sets limits on how efficiently heat energy can be converted into work.

Thermal Equilibrium : If two objects at different temperatures are placed in thermal contact (so that the heat energy can transfer from one to the other), the two objects will reach the same temperature, or become in thermal equilibrium. This explains why:
- Air molecules fill the room evenly, instead of all moving to one corner.
- A spoon reaches an equilibrium temperature, instead of one end being cold and one end being hot.
- Coffee, swirling in your cup, will eventually stop swirling. The coffee doesn't spontaneously cool down and start to swirl around.

17. A heat engine, such as a steam turbine, is a device which converts heat energy into mechanical
work. A heat pump requires an application of work to transfer heat energy from a low temperature to a higher temperature. Thus, the Second Law of Thermodynamics sets limits on how efficiently heat energy can be converted into work. A heat engine cannot convert all its heat to mechanical energy. No machine is ever 100% efficient.

18. Law of heat exchange: the sum of heat losses and gains in a closed system is zero. When two bodies of unequal temperature are mixed, the cold body absorbs heat (raising its temperature) and the hot body loses heat (lowering its temperature) until an equilibrium temperature is reached. Thermal equilibrium exists when two objects that are in themal contact with one another no longer affect each other's temperature.
Heat_Lost + Heat_Gain = 0
Objects are in thermal equilibrium when they are at the same temperature.

A Calorimeter is a device used to measure changes in thermal energy. A calorimeter is an insulated container used to make a precise measurement of heat exchange.

Energy Degradation refers to the fact that all energies degrade to heat energy. Degradation of energy occurs when other forms of energy becomes internal energy. Once it become internal energy, it is difficult to change it back to other forms. The implication of this is that the tranfer of tranformation of energy is not 100% efficient. ie not all the energy is useful.

19. Scientists explain melting in terms of the energy of molecules and the attraction of molecules for one another. A molecule is the smallest unit of a substance that is still clearly that substance. Every molecule has energy of movement, whether it is traveling, rotating, or merely vibrating in place.
In solids, each molecule is held in place by the attractive forces of its neighbors, so it moves very little. But adding heat to a solid gives its molecules more energy of movement, so that they rotate and vibrate more strongly. The space each molecule takes up therefore increases, because it is moving about in a greater area. This causes the solid that comprises these molecules to expand.

When the melting point for a substance has been reached, its molecules can gain too much energy to stay in one place. They break away from their fixed positions and move randomly. While the solid is melting, its temperature holds steady because all the heat applied to it goes to overcome the forces that hold the molecules in one place. Once the solid has melted completely, the heat applied to the substance again serves to speed up the movement of its molecules rather than to overcome the forces between them. The temperature of the substance therefore resumes its rise.

The stronger the attractive forces between the molecules of a solid, the higher its melting and boiling points will be. Very little energy is required to change oxygen from a solid to a liquid state because its molecules do not attract one another strongly. A great deal of energy, however, is required to change quartz from a solid to a liquid because the molecules of quartz are bound tightly together.

Some solids do not melt and become liquids under normal conditions. Dry Ice (solid carbon dioxide) is an example. At -110°F (-79°C) it changes from a solid to a gas. This process is called sublimation.

Created : 18 November 2000
Last modified : 26 November 2000
Author : Chad Silver email:Chaddysi@start.com.au
Site maintained by : Chad Silver